Modem communication systems, such as cellular systems, employ power amplifiers in their basestations, in order to communicate with subscribers that are distributed in cells. These power amplifiers are required to amplify Radio Frequency (RF) signals, such as signals used in communication systems that are required to transmit multiple signals, simultaneously. Multiple signals should be transmitted, for example, due to multiple users sharing the same frequency band, such as cellular systems that are operated in Code Division Multiple Access (CDMA) regimes. A basic condition for the proper operation of such power amplifiers is a stable feeding DC voltage, under any predetermined range of input RF signals and load.
A major problem that frequently occurs in basestation is the fluctuations in the feeding DC voltage, caused by inadequate battery charging and by load variations. This problem is apparent from practical requirements, which often define a range of supply voltage, for example, between 21 to 31 volts.
Conventional approaches for fulfilling such requirements employ high power built-in DC/DC converters which are bulky, expensive and power consuming. Such high power built-in DC/DC converters reduce the overall efficiency of the power amplifiers by 15% (typically). Therefore, this problem should be overcome by using a more efficient solution.
The approaches described above have not yet provided satisfactory solution to the problem of providing a stable power output to power amplifiers, operated with signals having a large peak-to-average ratio under unstable supply voltage conditions, while eliminating the need for DC input voltage stabilization.
It is an object of the present invention to provide a method and apparatus for providing a power amplifier having a stable power output, while operating under unstable DC supply voltage conditions.
It is another object of the present invention to provide a method and apparatus for providing a power amplifier having a stable power output while operating under unstable DC supply voltage conditions, with improved efficiency.
It is still another object of the present invention to provide a method and apparatus for providing a power amplifier having a stable power output while operating under unstable DC supply voltage conditions, which is compact and cost effective.
It is yet another object of the present invention to provide a method and apparatus for providing a power amplifier that can output a non-distorted RF signal of given power, independently of fluctuations and/or variations in the voltage of the DC power supply, within a predetermined allowable range.
Other objects and advantages of the invention will become apparent as the description proceeds.